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Thermodynamics: gas for stirling engine + liquid with high density

  1. Feb 15, 2006 #1

    for the ones that don't like to read much (:smile:): the basic point is that I need a gas that gives as much pressure as possible with a temperature increase and a constant volume and that is easy to get my hands on; and a liquid with a high density (like mercury or something) that has a high boiling pont (preferably higher than 100°C), doesn't damage latex and isn't poisenous/dangerous.

    I plan on building a model stirling engine (an engine that runs on heat) I've searched the web and found a nice, easy, little engine called the RotaColaSola engine, it should work on solar heat. (link: the original one (RotaColaSola) and the improved one (SexBalloon engine).
    I would like to build the SexBalloon-type of engine (using balloons, no condoms :tongue: ) and I've started saving tin cans (empty catfood cans) because they are bigger and I have a bigger supply of them :smile:.

    Now the actual question-part: While I'm waiting until I've got enough tin cans, I thought of a few improvements:
    - If I would use a gas that, given a constant volume, produces more pressure with an equal temperature increase than plain air. (if it's explained badly I'll give an example: if the temperature increases with 10degC, the pressure of gas X increases with 10% while the pressure of regular air only increases with 5% -> twice as much power?) This will cause the liquid in the balloon to be pressed up more wich should create more power. (my physics-teacher said something about hydrogen or helium?...)
    - If I replace the water with a liquid that has higher density, the difference in weight will be greater when a same amout of liquid is pushed into the other reservoir and thus increasing the power. (example: if 1cc of water is moved, the weight that is moved is 1gram; if 1cc of liquid X is moved, the weight that is moved is equal to 2grams -> twice the power?) *note*: the boiling temperature would need to be as high as possible (the liquid must stay a liquid when heated with sun or with candle/flame/...)

    I know that this forum is packed with physics-geniouses :wink: so if someone could please confirm the above or give other advice...
    And does anyone know gasses and liquids that meet the above requirements, are easy to get and aren't dangerous?


    The Crazy Noob
  2. jcsd
  3. Feb 15, 2006 #2
    Just make a very concentrated solution of NaCl will be very dense and has pretty much infinite solubility so you can make it as dense as you like. Don't really know anything about gases off hand though.
  4. Feb 16, 2006 #3
    lol, that just sounds so logical, can't believe i didn't think of that :blushing: :smile: (btw: the density of NaCl is 2.17 g/cm3, but i could use annything that is soluble in water...)

    Thanks for the tip, now i just need a gas :smile:
  5. Mar 10, 2006 #4
    ** bump **
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